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diff src/fftw-3.3.5/doc/FAQ/fftw-faq.html/section4.html @ 127:7867fa7e1b6b
Current fftw source
| author | Chris Cannam <cannam@all-day-breakfast.com> |
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| date | Tue, 18 Oct 2016 13:40:26 +0100 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.5/doc/FAQ/fftw-faq.html/section4.html Tue Oct 18 13:40:26 2016 +0100 @@ -0,0 +1,64 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<html> +<head><title> +FFTW FAQ - Section 4 +</title> +<link rev="made" href="mailto:fftw@fftw.org"> +<link rel="Contents" href="index.html"> +<link rel="Start" href="index.html"> +<link rel="Next" href="section5.html"><link rel="Previous" href="section3.html"><link rel="Bookmark" title="FFTW FAQ" href="index.html"> +</head><body text="#000000" bgcolor="#FFFFFF"><h1> +FFTW FAQ - Section 4 <br> +Internals of FFTW +</h1> + +<ul> +<li><a href="#howworks" rel=subdocument>Q4.1. How does FFTW work?</a> +<li><a href="#whyfast" rel=subdocument>Q4.2. Why is FFTW so fast?</a> +</ul><hr> + +<h2><A name="howworks"> +Question 4.1. How does FFTW work? +</A></h2> + +The innovation (if it can be so called) in FFTW consists in having a +variety of composable <i>solvers</i>, representing different FFT algorithms and implementation strategies, whose combination into a +particular <i>plan</i> for a given size can be determined at runtime according to the characteristics of your machine/compiler. +This peculiar software architecture allows FFTW to adapt itself to +almost any machine. +<p> +For more details (albeit somewhat outdated), see the paper "FFTW: +An Adaptive Software Architecture for the FFT", by M. Frigo and +S. G. Johnson, <i>Proc. ICASSP</i> 3, 1381 (1998), also available at <A href="http://www.fftw.org">the FFTW web page</A>. +<h2><A name="whyfast"> +Question 4.2. Why is FFTW so fast? +</A></h2> + +This is a complex question, and there is no simple answer. In fact, +the authors do not fully know the answer, either. In addition to many +small performance hacks throughout FFTW, there are three general +reasons for FFTW's speed. +<ul> +<li> FFTW uses a variety of FFT algorithms and implementation styles +that can be arbitrarily composed to adapt itself to +a machine. See <A href="#howworks">Q4.1 `How does FFTW work?'</A>. +<li> FFTW uses a code generator to produce highly-optimized +routines for computing small transforms. + +<li> FFTW uses explicit divide-and-conquer to take advantage +of the memory hierarchy. +</ul> +For more details (albeit somewhat outdated), see the paper "FFTW: +An Adaptive Software Architecture for the FFT", by M. Frigo and +S. G. Johnson, <i>Proc. ICASSP</i> 3, 1381 (1998), available along with other references at +<A href="http://www.fftw.org">the FFTW web page</A>. <hr> +Next: <a href="section5.html" rel=precedes>Known bugs</a>.<br> +Back: <a href="section3.html" rev=precedes>Using FFTW</a>.<br> +<a href="index.html" rev=subdocument>Return to contents</a>.<p> +<address> +<A href="http://www.fftw.org">Matteo Frigo and Steven G. Johnson</A> / <A href="mailto:fftw@fftw.org">fftw@fftw.org</A> +- 30 July 2016 +</address><br> +Extracted from FFTW Frequently Asked Questions with Answers, +Copyright © 2016 Matteo Frigo and Massachusetts Institute of Technology. +</body></html>